Doxepin and Nordoxepin, Serum
Use
This test is useful for monitoring doxepin therapy, evaluating potential doxepin toxicity, and evaluating patient compliance. Doxepin is recommended for treating psychoneurotic patients with depression or anxiety, or with depression or anxiety associated with alcoholism or organic disease. The test measures both doxepin and its major metabolite nordoxepin, providing insights into therapeutic efficacy (optimal efficacy occurs at combined serum concentrations between 50 and 150 ng/mL) and toxicity (cardiac dysrhythmias occur at concentrations more than 500 ng/mL).
Special Instructions
Therapeutic ranges and interpretation should be based on trough specimens, collected immediately before the next scheduled dose. Ensure serum is separated from cells within 2 hours of collection to prevent falsely elevated results. Specimens from serum gel tubes are not acceptable due to potential drug absorption on gel, leading to falsely decreased concentrations. Complete a Therapeutics Test Request form if not ordering electronically.
Limitations
This test cannot be performed on whole blood. Serum must be separated from cells within 2 hours of collection to ensure accurate measurement. Failure to do so may result in falsely elevated levels due to drug release from red blood cells. Specimens obtained from serum gel tubes are not accepted as the drug can absorb on the gel and lead to falsely decreased concentrations. Evaluations should consider clinical context as some individuals may respond outside the therapeutic range or show toxicity within it.
New York Approved
Methodology
Mass Spectrometry (LC-MS/MS)
Biomarkers
LOINC Codes
- 43122-1
- 3579-0
- 3862-0
- 3582-4
Result Turnaround Time
3-5 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL
Minimum Volume
0.25 mL
Container
Plastic vial
Collection Instructions
Collect specimen immediately before the next scheduled dose (minimum 12 hours after last dose). Centrifuge and aliquot serum into a plastic vial. Serum must be separated from cells within 2 hours of collection.
Causes for Rejection
Gross hemolysis, gross lipemia, gross icterus, serum gel tubes not accepted.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 7 days |
| Refrigerated | 28 days |
| Frozen | 28 days |